Corrosion inhibitors containing amphoteric surfactants

ABSTRACT

The invention relates to the use of compositions containing metal salts of compounds of the formula (1) 
     
       
         
         
             
             
         
       
     
     in which R 1  is C 1 - to C 29 -alkyl, C 2 - to C 29 -alkenyl, C 6 - to C 30 -aryl or C 7 - to C 30 -alkylaryl, and amphoteric surfactants as corrosion inhibitors.

The present invention is described in the German priority application No. 10 2007 041 217.9 filed Aug. 31, 2007, which is hereby incorporated by reference as is fully disclosed herein.

The present invention relates to a process for corrosion inhibition on and in apparatuses for conveying and transporting hydrocarbons in oil production and processing by adding a metal salt of N-acylmethionine and an amphoteric surfactant to the corrosive system.

In industrial processes in which metals come into contact with water or with oil/water two-phase systems, there is the danger of corrosion. This is particularly pronounced if the aqueous phase has a high salt content, as in oil extraction and processing processors, or is acidic due to dissolved acid gases, such as carbon dioxide or hydrogen sulfide. The exploitation of a deposit and the processing of oil are therefore not possible without special additives for protecting the equipment used.

Although suitable corrosion inhibitors for oil production and processing have long been known, they are unacceptable in future for offshore applications for reasons relating to environmental protection.

As typical corrosion inhibitors of the prior art, amides, amidoamines or imidazolines of fatty acids and polyamines have an extremely good oil solubility and, owing to poor partitioning, are therefore present only in low concentration in the corrosive water phase. Accordingly, these products must be used at a high dose in spite of their poor biodegradability.

Quaternary alkylammonium compounds (quats) are alternative corrosion inhibitors of the prior art, which also have biostatic properties in addition to the corrosion-inhibiting properties. In spite of improved water solubility, the quats have a substantially reduced film persistence, for example compared with the imidazolines, and therefore likewise lead to effective corrosion protection only in relatively high doses. The strong algae toxicity and the moderate biodegradability are increasingly limiting the use of quats to ecologically insensitive fields of use.

U.S. Pat. No. 4,240,823 describes N-acylmethionine derivatives which are used as growth regulators in the area of crop protection.

JP-A-8 337 562 and JP-A-8 337 563 describe N-acylamino acids and their alkali metal salts, which can also be used as corrosion inhibitors.

JP-A-49 026 145 describes alkali metal salts of N-acylamino acids, which salts can be used as corrosion inhibitors. N-Lauroylglycine sodium salt is mentioned as an example.

DE-10 2006 002 784 discloses N-acylmethionine ammonium salts which have an excellent effect as corrosion inhibitors and show good biodegradability and reduced toxicity. A disadvantage of these compounds is, however, their complicated preparation and the associated relatively high production costs.

It was an object of the present invention to provide novel corrosion inhibitors which, in combination with improved corrosion protection, also afford improved biodegradability and lower toxicity in comparison with the corrosion inhibitors of the prior art in addition to good water solubility. Furthermore, the novel corrosion inhibitors should be capable of being produced at an economically acceptable price.

It has now surprisingly been found that metal salts of N-acylmethionine as a mixture with amphoteric surfactants have an excellent effect as corrosion inhibitors and show good biodegradability and reduced toxicity. Owing to a synergistic effect between the metal salt of N-acylmethionine and nonionic surfactant, the dosages can be substantially reduced in comparison with the prior art, with the result that the novel corrosion inhibitor mixtures are also advantageous economically.

The invention therefore relates to the use of compositions containing metal salts of compounds of the formula (1)

in which R¹ is C₁- to C₂₉-alkyl, C₂- to C₂₉-alkenyl, C₆- to C₃₀-aryl or C₇- to C₃₀-alkylaryl, and amphoteric surfactants as corrosion inhibitors.

The invention furthermore relates to a process for inhibiting corrosion on metal surfaces, in particular of iron-containing metals, by adding at least one metal salt of compounds of the formula (1) and an amphoteric surfactant to a corrosive system which is in contact with the metal surfaces.

The invention furthermore relates to compositions containing at least one metal salt of a compound of the formula (1) and at least one amphoteric surfactant.

The invention furthermore relates to the use of metal salts of compounds of the formula (1) together with amphoteric surfactants as metal processing compositions. Here, the compositions according to the invention also afford very good corrosion protection even under strong mechanical load, such as during grinding, cutting and drilling of metal workpieces.

Corrosive systems in the context of this invention are preferably liquid/liquid or liquid/gaseous multiphase systems consisting of water and hydrocarbons which contain corrosive constituents, such as salts and acids, in free and/or dissolved form. The corrosive constituents may also be gaseous, such as, for example, hydrogen sulfide and carbon dioxide.

Hydrocarbons in the context of this invention are organic compounds which are constituents of mineral oil/natural gas, and the secondary products thereof. Hydrocarbons in the context of this invention are also readily volatile hydrocarbons, such as, for example, methane, ethane, propane and butane. For the purposes of this invention, these also include the further gaseous constituents of mineral oil/natural gas, such as, for example, hydrogen sulfide and carbon dioxide.

Preferred surfactants are those which, in a concentration of 0.5% by weight in water, produce a surface tension of this aqueous solution of not more than 55 mN/m, particularly preferably of not more than 50 mN/m and especially not more than 45 mN/m.

In a further preferred embodiment of the invention, R¹ is C₃- to C₂₃-alkyl, C₃- to C₂₃-alkenyl, C₆- to C₂₄-aryl or C₇- to C₂₅-alkylaryl, in particular an alkyl or alkenyl group having 7 to 17 carbon atoms.

Suitable amphoteric surfactants are described in detail in U.S. Pat. No. 5,106,609, U.S. Pat. No. 6,169,060 and WO 9949008. Particularly suitable amphoteric (zwitterionic) surfactants correspond to the formulae (2) to (14):

in which R is an alkyl, alkenyl, hydroxyalkyl or alkylaryl group having 4 to 22 carbon atoms, each radical R1, independently of one another, is an alkyl or hydroxyalkyl group having 1 to 3 carbon atoms or two R1 groups are linked to one another via an —O or —NH group with ring formation, A is an alkylene group having 2 to 4 carbon atoms or mixtures thereof, and x is a number from 0 to 10. M is H, alkali metal, alkaline earth metal, ammonium or alkanolammonium and m and n, independently of one another, are numbers from 1 to 4.

Particularly preferred betaines are compounds of the formulae (2) or (3) with R═C₈-C₂₂-alkyl or -alkenyl, R1=CH₃ or hydroxyethyl or hydroxypropyl, n=1 or 3, m=3 and x=0. Examples are C_(12/14)-alkyldimethylcarboxybetaine, C_(12/14)-alkylamidopropyl-N,N-dimethyl-N-carboxylmethylbetaine, stearyldimethylcarboxybetaine, behenyldimethylcarboxybetaine, oleyldi(hydroxyethyl)carboxybetaine or oleyidimethyl-3-carboxypropylbetaine.

Particularly preferred compounds of the formulae (4) to (7) are amphoacetates and amphopropionates with R═C₈-C₁₈-alkyl or -alkenyl, x=0, m=2, n=1 or 3 and M=H, Na, K, alkanolammonium. Examples are sodium lauroamphoacetate, sodium lauroamphodiacetate, sodium lauroamphopropionate, sodium lauroamphodipropionate, octylaminopropionic acid, octyliminodipropionic acid, cocoaminopropionic acid and cocoiminodipropionic acid.

Sulfobetaines of the formulae (8) to (11) are particularly preferred with R═C₈-C₁₈-alkyl or -alkenyl, R1=CH₃ or hydroxyethyl or hydroxypropyl, n=1, 3 or 4, x=0, m=2 and M=H, Na, K, alkanolammonium. Examples are cocodimethylsulfopropylbetaine, octyldimethyldi(hydroxyethyl)sulfopropylbetaine and stearyldimethylsulfobutylbetaine.

Particularly preferred amine oxides of the formulae (12) and (13) are C₈-C₁₈-alkyldimethylamine oxides and C₈-C₁₈-alkoxyethyldihydroxyethylamine oxides, such as cocodimethylamine oxide, stearyldimethylamine oxide, lauryldi(hydroxylethyl)amine oxide, and myristyldimethylamine oxide.

Alkyl- or alkenylimidazoliniumbetaines of the formula (14) are particularly preferred with R═C₇-C₁₇-alkyl or -alkenyl. Examples are coconut fatty acid (hydroxyethylimidazoline)carboxymethylbetaine, oleic acid (hydroxyethylimidazoline)carboxymethylbetaine and tall oil fatty acid (hydroxyethylimidazoline)carboxymethylbetaine.

The compositions according to the invention can be used alone or in combination with other known corrosion inhibitors. In general, the composition according to the invention is used in an amount such that sufficient corrosion protection is obtained under the given conditions.

Preferred concentrations in which the compositions according to the invention are used are from 5 to 5000 ppm, preferably from 10 to 1000 ppm, in particular from 15 to 150 ppm. The mixing ratio between metal salt of the compound 1 and amphoteric surfactant is preferably from 1:9 to 9:1, in particular from 3:7 to 7:3.

Mixtures of the compositions according to the invention with other corrosion inhibitors of the prior art are also particularly suitable as corrosion inhibitors.

EXAMPLES

General method for the preparation of metal salts of N-acylmethionine

In a standard stirred apparatus, 1 mol of DL-methionine in 300 ml of water are neutralized with 50% strength aqueous metal hydroxide solution. 1 mol of carboxylic acid chloride is metered into the resulting solution at 15-20° C., the pH being kept at 10-13 by simultaneous metering of 15% strength aqueous metal hydroxide solution. The reaction solution is stirred for a further 3 h at room temperature. The resulting metal salt of N-acylmethionine is characterized by means of the alkali number (AN) and active substance content. Stated percentages are percentages by weight, based on the weight of the salt according to the invention.

Example 1 N-Cocoyl-DL-methionine Sodium Salt (Comparison)

N-Cocoyl-DL-methionine sodium salt having an active substance content of 40% and an AN=65 mg KOH/g was obtained from coconut fatty acid chloride, DL-methionine and sodium hydroxide.

Example 2 N-Oleoyl-DL-methionine Potassium Salt (Comparison)

N-Oleoyl-DL-methionine potassium salt having an active substance content of 40%

and an AN=56 mg KOH/g was obtained from oleoyl chloride, DL-methionine and potassium hydroxide.

Example 3 Corrosion Inhibitor Mixture 1

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 40 g of a 20% strength solution of behenyldimethylcarboxybetaine and 20 g of butylglycol.

Example 4 Corrosion Inhibitor Mixture 2

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 8 g of octylaminopropionic acid, 20 g of butylglycol and 32 g of water.

Example 5 Corrosion Inhibitor Mixture 3

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 40 g of a 20% strength aqueous solution of cocodimethylsulfopropylbetaine and 20 g of butylglycol.

Example 6 Corrosion Inhibitor Mixture 4

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 40 g of a 20% strength aqueous solution of lauryldi(hydroxyethyl)amine oxide and 20 g of butylglycol.

Example 7 Corrosion Inhibitor Mixture 5

40 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 8 g of tall oil fatty acid (hydroxyethylimidazoline)-carboxymethylbetaine, 20 g of butylglycol and 32 g of water.

Example 8 Corrosion Inhibitor Mixture 6

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 40 g of a 20% strength aqueous solution of behenyldimethylcarboxybetaine and 20 g of butylglycol.

Example 9 Corrosion Inhibitor Mixture 7

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 8 g of octylaminopropionic acid, 20 g of butylglycol and 32 g of water.

Example 10 Corrosion Inhibitor Mixture 8

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 40 g of a 20% strength aqueous solution of cocodimethylsulfopropylbetaine and 20 g of butylglycol.

Example 11 Corrosion Inhibitor Mixture 9

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 40 g of a 20% strength aqueous solution of lauryldi(hydroxyethyl)amine oxide and 20 g of butylglycol.

Example 12 Corrosion Inhibitor Mixture 10

40 g of N-oleoyl-DL-methionine potassium salt from example 2 were mixed with 8 g of tall oil fatty acid (hydroxyethylimidazoline)carboxymethylbetaine, 20 g of butylglycol and 32 g of water.

Example 13 Corrosion Inhibitor Mixture 11

55 g of N-cocoyl-DL-methionine sodium salt from example 1 were mixed with 2 g of tall oil fatty acid (hydroxyethylimidazoline)-carboxymethylbetaine, 20 g of butylglycol and 23 g of water.

Activity of the Compounds According to the Invention as Corrosion Inhibitors

The compounds according to the invention were tested as corrosion inhibitors in the Shell wheel test. Coupons of C steel (DIN 1.1203 with 15 cm² surface area) were immersed in a salt water/petroleum mixture (9:1, 5% strength NaCl solution adjusted to pH 3.5 with acetic acid) and exposed to this medium at a speed of 40 rpm at 70° C. for 24 hours. The inhibitor dose was 50 ppm of a 24% solution of the inhibitor. The protection values were calculated from the decrease in the mass of the coupons, based on a blank value.

In the following tables, “comparison 1” designates a commercially available residue amine quat based on dicocosalkyl dimethylammonium chloride, “comparison 2” a commercially available imidazoline salt based on oleic acid diethylenetriamine and “comparison 3” an example from DE-10 2006 002 784 (morpholinium salt of N-cocoyl-DL-methionine, corrosion inhibitor of the prior art).

TABLE 1 (Shell wheel test) Example Corrosion inhibitor ø protection % Comparison 1 Standard quat 28 Comparison 2 Oleic acid DETA imidazoline 70 Comparison 3 Morpholinium salt of 75 N-cocoyl-DL-methionine Comparison 4 from example 1 67 Comparison 5 from example 2 69 14 from example 3 86 15 from example 4 80 16 from example 5 89 17 from example 6 89 18 from example 7 93 19 from example 8 86 20 from example 9 81 21 from example 10 90 22 from example 11 89 23 from example 12 94 24 from example 13 82

As is evident from table 1, the compositions according to the invention have very good corrosion inhibition properties at a very low dose and in some cases even substantially surpass the activity of the inhibitors of the prior art.

In comparison with example 18, example 24 shows that the synergistic effect of the metal salt of N-acylmethionine in combination with an amphoteric surfactant decreases at a ratio of >9:1 but is still present.

TABLE 2 Biodegradability (OECD 306) and toxicity (EC₅₀ Skeletonema Costatum) of selected corrosion inhibitors according to the invention Biodegradability Toxicity Example Corrosion inhibitor [%] EC₅₀ [mg/l] Comparison 1 Standard quat 15.2 0.57 Comparison 2 Oleic acid DETA 6.8 0.33 imidazoline 25 from example 3 62.4 58.1 26 from example 4 81.0 71.9 27 from example 7 42.5 30.1 28 from example 9 77.5 68.5

As can clearly be seen from table 2, the compounds according to the invention exhibit improved biodegradability and lower toxicity compared to the comparative examples from the prior art. 

1. A method for inhibiting corrosion on a metal surface, said method comprising contacting said metal surface with a composition comprising a metal salt of the compound of the formula (1)

in which R¹ is C₁- to C₂₉-alkyl, C₂- to C₂₉-alkenyl, C₆- to C₃₀-aryl or C₇- to C₃₀-akylaryl, and an amphoteric surfactant.
 2. The method of claim 1, wherein R¹ is an alkyl or alkenyl group having 7 to 17 carbon atoms.
 3. The method of claim 1, wherein the metal salt is an alkali metal salt.
 4. The method of claim 1, wherein the amphoteric surfactant is selected from the group consisting of a compound of the formulae (2) to (14)

in which R is C₄- to C₂₂-alkyl, C₄- to C₂₂-alkenyl or C₄- to C₂₂-alkylaryl R1 is C₁- to C₃-alkyl, C₁- to C₃-hydroxyalkyl R3 is methyl or -A-(OA)_(n)-OH R4 is -A-(OA)_(n)-OH A is a C₂- to C₄-alkylene group m is a number from 1 to 4 n is a number from 1 to 4 x is a number from 0 to 10 M is H, an alkali metal, alkaline earth metal, ammonium or alkanolammonium.
 5. The method of claim 1, wherein a total amount of metal salt to amphoteric surfactant is from 5 to 5000 ppm.
 6. The method of claim 1, wherein a weight ratio of metal salt to amphoteric surfactant is from 1:9 to 9:1.
 7. The method of claim 1, wherein said composition further comprises a hydrocarbon and said metal surface is an apparatus for conveying and transporting the hydrocarbon.
 8. The method of claim 1, wherein the composition further comprises a metal processing composition.
 9. A composition containing at least one metal salt of a compound of the formula (1)

in which R¹ is C₁- to C₂₉-alkyl, C₂- to C₂₉-alkenyl, C₆- to C₃₀-aryl or C₇- to C₃₀-alkylaryl, and at least one amphoteric surfactant.
 10. The composition as claimed in claim 9, wherein a weight ratio of metal salt to amphoteric surfactant is from 9:1 to 1:9. 